In present oil distribution and marketing, a major problem is moisture in the hydrocarbon fuel supplied to the consumer. There exist many methods for removing moisture from the fuel prior to dispensing. One widely used method is to flow the fuel through a filter/separator.
A filter/separator is normally composed of two stages. The first stage, called the coalescer, removes dirt and coalesces finely dispersed moisture into discrete water droplets. Most of the water droplets fall by gravity to a sump and are drained. The second stage, called the separator, removes finer water droplets which are comingled with the fuel. In the first stage, disposable coalescer elements are used. Either paper elements or "Teflon" elements may be used in the second stage as separator elements.
The stages will remove dirt and water from fuel, such as that used in aviation, effectively as long as the elements are structurally sound and have not been contaminated with surfactants. The elements in both stages are normally changed on an elapsed time basis provided that a gravimetric millipore test on the effluent fuel remains satisfactory and the elements maintain a predetermined flow rate. Once the elements become plugged with particulate matter the pressure drop across the filter/separator will change indicating that the elements are no longer effective and must be replaced, in addition to changing the elements on an elapsed time basis.
If the coalescer elements and separator elements become contaminated with surfactants, dispersed water will not be removed plus fine particulate matter may not be removed. Of the two types of separator elements described, paper separator elements are preferred since they have superior filtration ability and are less susceptible to damage during installation. In addition, paper separator elements have a lower initial cost as compared to "Teflon" separator elements. However, there is presently no convenient test for surfactant contamination of either the coalescers or the paper separator elements.